The present invention generally relates to seat belt systems and more particularly to a pretensioner or belt tightener, which during an accident moves a seat belt buckle to a position that tends to tighten a lap belt and/or shoulder belt of a seat belt system (typically a 3-point seat belt system) about an occupant to be protected.
Pretensioners, which are often called belt tighteners, are known in the art and have been used in vehicles for many years. In general, a pyrotechnically driven piston is forced down a narrow tube at the onset of a vehicular accident. The piston is attached to an anchor cable, the other end of which is secured to the seat belt buckle. The buckle in turn is connected to a seat belt tongue, which is operatively attached to the lap belt and shoulder belt of, for example, a 3-point seat belt system. Quite often in buckle pretensioners, a portion of the cable is looped about a pulley or casting that provides a channel for the cable. This type of hardware supports the cable and also functions as a direction-changing element for adjacent sections of the cable. The hardware permits the piston to move down a tube that is oriented at an acute angle relative to an extending piece of cable connected to the buckle. Pretensioners will typically also include a housing element or bracket that is useful in mounting the pretensioner to, for example, a portion of the vehicle structure or seat structure. The housing element or bracket also includes an element that aids in positioning the cable/buckle portion of the cable assembly to meet buckle zone requirements as specified by NHTSA.
The present invention provides a lightweight, cost effective pretensioner that avoids the use of expensive castings.
It is an object of the present invention to provide a pretensioner having principle portions made from tubes.
It is a further object of the present invention to provide thermal resistance to the device during extreme temperatures as can occur during a fire, either during transportation of the device to the vehicle assembly plant or in the motor vehicle itself. This protection is accomplished by way of the steel tubing in contrast to traditional zinc die-cast components which, as used in the prior art, house a pyrotechnic device called a micro gas generator. The pyrotechnic device when subjected to extreme heat or a heat source, such as a flame, can begin to soften and melt prior to the auto-ignition of the propellant, causing molten metals to be projected from the device. The glass transition temperature of the steel tubing used in the present invention, which houses the gas generator, is several times higher than that of the zinc die-cast, reducing the potential of injury to either the occupant or the emergency personnel.
An additional aspect of this device is to provide staggered and measured energy management of the buckle head's (seat belt buckle) acceleration/deceleration at the end of pretensioning. Excessive acceleration has been demonstrated to damage internal components of the buckle head, requiring several countermeasures to be used to mitigate these effects. With the present invention the first deceleration feature is a ferrule that contacts the tapered section of the main tube, yielding the tubing, slightly absorbing energy. The second deceleration feature is a deformable bulb near the cable guide tube, which yields as a buckle connector contacts the end of the tube, providing additional energy absorption. The final deceleration feature in this sequence is the piston itself, which may also contact the tapered end of the main tube, preventing it from leaving the end and causing reduced performance in the retention of the buckle position.
A further object of this invention is to provide a more effective cable transition path. As can be seen in the prior art most current pretensioners include a pulley or cast, cable channel, which acts as a direction-changing element. The cable, when pulled about these devices, exhibits increased friction levels that affect pretensioner performance and reduce its efficiency. Further, the use of a hardened material to provide the cable path as opposed to a softer material, such as a zinc casting, is that the cable (which is for example a twisted wire rope) will no longer dig into the softer supporting material such as zinc. The cable path in the present invention is provided by a curved tube of sufficiently large diameter to overcome the deficiencies of the prior art.
Accordingly the invention comprises: a pretensioner for use with a seat belt system, the pretensioner comprising: a straight first tube having a cylindrical wall, a first end and a second end, at least one of the first end or the second end being open; the first tube includes a first opening in the wall to receive a second tube, the second tube having a first end portion, a second end portion and a medial portion, the medial portion configured to have a circular curvature of radius R1; the second end portion is situated so that its center is collinear with a central axis extending through the center of the first tube and wherein an axis extending through the center of the first end portion is arranged at an acute angle relative to the central axis; a pyrotechnic element is provided at one end of the first tube to provide products of combustion to drive a piston down the first tube, the motion of the piston moving a cable in a direction to move a seat belt buckle to reduce belt slack about an occupant to be protected, and a housing or bracket portion configured to attach the pretensioner to a mounting surface.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.